A woman carries water she drew from a pool of a drying tributary of the Amazon River as the season drought worsens to one of the worst in recent years, in Parana do Paraua, Brazil, on Nov. 24, 2009. After a rainy season that caused some of the worst flooding in recent history, the seasonal drought that followed proved to be especially bad as well.

The International Water Management Institute (IMWI) predicts that by 2025 about 1.8 billion people will live in places suffering from severe water scarcity. Many already do.

"Take the Horn of Africa for example: Somalia's population has risen roughly fivefold since the middle of the 20th century," Jeffrey Sachs, director of the Earth Institute at Columbia University, said at an Oct. 17 meeting of academics. "Precipitation is down roughly 25 percent over the last quarter century. There's a devastating famine under way right now after two years of complete failure of rains, and [there is] the potential that this is entering a period of long-term climate change."

Amit Dave / Reuters

People gather to get water from a well in the village of Natwarghad, India, on June 1, 2003, in the midst of a severe drought. Dams, wells and ponds went dry across the western and northern parts of Gujarat, forcing people to wait for hours around village ponds for the irregular state-run water tankers to show up as the temperature soared to over 110 degrees.

Conflicts over water shortages could play out as class warfare as the rich commandeer the water and other resources of the poor, Upmanu Lall, director of the Columbia Water Center, warned at the academics meeting.

But solutions are possible.

“Nations need to find ways to deliver food security across regions facing water scarcity and ensure that poor farmers who underpin global food production are resilient enough to cope with future challenges,” IMWI says.

Ahmad Masood / Reuters

An Afghan man pushes a hand cart with water containers near a public water pump in Kabul on Jan. 13, 2010.

Increasing agricultural productivity through effective management of water resources not only helps eliminate hunger, it also leads to long-term increases in rural wealth and lifts poor farmers beyond subsistence-level farming, IMWI says.

"There's quite a bit of land that could produce food if we had the water to go with it," said Lester Brown, an environmental analyst who heads the Earth Policy Institute in Washington. "It's water that's becoming the real constraint."

A resident shows the water she gets at her home in a poor neighborhood in Mexico City on Dec. 17, 2009. A lack of rainfall and the growing needs of a thirsty capital city full of leaky pipes is draining the many lakes that once covered Mexico City's vast urban plain. City residents know their water by the brownish color as it leaves the spout.